IP addresses: A wasted resource?

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WHEN IPV4 WAS adopted, 4 billion sounded like an awful lot of IP addresses.

Today, faced with the exhaustion of IPv4 address space within five to 15 years, we are turning to a new generation of protocols and a new addressing scheme to fill our seemingly insatiable desire for more and better networks and devices.

What happened to all of those old addresses? Were they squandered? Common estimates put the efficiency of address usage at 25 percent to 50 percent, which would mean that as many as 50 percent or 75 percent of available IPv4 addresses remain unused, sitting idly in sparsely populated subnets within the allocations of early adopters.

That's probably not so, said Richard Jimmerson, chief information officer at the American Registry for Internet Numbers, one of five Regional Internet Registries responsible for doling out address space. 'A lot of address space is in use inside networks that is not announced on Internet routing tables, for one reason or another,' he said.

These addresses sit, not necessarily idle, behind firewalls and are not reachable from the Internet. The U.S. government has entire secret networks that are not announced, Jimmerson said. 'That's a large amount of address space.'

Of course, the original IPv4 addresses were not evenly distributed, forcing users in Asia and Europe to turn to IPv6 earlier than those of us in address-rich North America.

Some of this inequity has been mitigated by tools, such as Network Address Translation, which have helped stretch available space. But on the whole, we have done a pretty good job of managing the original 4 billion addresses available through IPv4, Jimmerson said. 'We have to be approaching 4 billion devices on the Internet now.'

About the Author

William Jackson is freelance writer and the author of the CyberEye blog.